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TAS3251EVM: PFFB follow-up questions- especially regarding the error in the EVM.

UA&A_CodyDowling
Intellectual 996 points
Part Number: TAS3251EVM
Other Parts Discussed in Thread: TAS3251, TPA3251

Tool/software:

TI Team, 

We are implementing PFFB in the TAS3251, but have two questions:

  1. Is there a spice model for the TAS3251 (or really any of a similar architecture amplifier) with which we can simulate the PFFB loop gain, phase margin, etc.? The application note by the venerable Mr. Beardsworth indicates that measuring overshoot is a good way to tune these parameters- but it would be preferable to get a little closer with the initial values, if possible, through simulation.
  2. I found this post: https://e2e.ti.com/support/audio-group/audio/f/audio-forum/1220157/tpa3223-does-the-tpa3223-can-add-the-pffb?tisearch=e2e-sitesearch&keymatch=PFFB# that seems to indicate the EVM was wired incorrectly... has this been addressed/fixed? If so, what revision of the board/document can we reference to make sure we don't implement a known bug?

  • 0
    TI__Genius 14155 points

    Hello, 

    Apologies for the delay. Please expect a response early next week.

    Regards,
    Sydney Northcutt

  • 0 in reply to Sydney Northcutt
    TI__Genius 9175 points

    Hello,

    There is no spice model for this amp and the EVM has not been changed. This topology wasn't tested or designed for this specific part, but you can refer to this app note for information on how PFFB is implemented on TPA32xx devices.

    Regards,

    Ramsey

  • 0
    Intellectual 996 points

    Hi , , 

    Thank you for your responses, but unfortunately this doesn't get us any closer to a solution. We've traced out  the issues in the documentation for this EVM and found the error there. The hardware appears, at some point, to be wired correctly. So, we can set this issue aside and focus on the PFFB topic.


    In both versions of the app note on PFFB do not offer detailed information about how we can design our own feedback loop- but rather suggestions which stipulate different filter values than will use in our design and result in gains which are not appropriate for our application. It also suggests that the TPA3251 (the back-end IC in the TAS3251) is a bit of an "unknown" and therefore we should place the typical values in the design and then use the ringing on the outputs to determine stability. Since we cannot use those values for this application, we aren't able to do that. 

    Since we are under MNDA with TI, would it be possible to share the details of the feedback loop inside the TPA3251 with us so that we can design the outer feedback loop around it and at least land closer to the final values we'll need to ensure stability? Even just the poles and zeros of the internal filter would be helpful. 

  • 0 in reply to UA&A_CodyDowling
    TI__Genius 9175 points

    Hello,

    I will send you an email and we can discuss further there.

    Regards,

    Ramsey